Armature for an electric machine

ABSTRACT

In a press fit of a component on a shaft of the prior art, stresses that can damage the component remain in the mounted component.  
     An armature ( 15 ) of the invention has a component ( 1 ), to be mounted on the shaft ( 10 ), that has a taper ( 7 ) in the internal diameter; the taper engages a knurled feature ( 11 ) on the shaft ( 10 ), and the initial stresses can lessen at least in part over the course of time.

PRIOR ART

[0001] The invention is based on an armature for an electrical machine as generically defined by the preamble to claim 1.

[0002] From U.S. Pat. No. 4,886,392, a rotor with a shaft that has a knurled feature and smooth regions on a surface of the shaft is already known; the shaft has approximately the same external diameter both in the region of the knurled feature and in the smooth regions. The rotor, which is slipped onto the shaft, however, has no taper in the internal diameter, which is disposed in the region of the knurled feature.

[0003] From U.S. Pat. No. 5,625,511, a stator with a shaft is known, in the middle of which shaft a knurled feature is provided. On the far side of the knurled feature on the shaft there is a smooth region, which has the same external diameter as the knurled feature and can be used to guide the stator, which is secured on the shaft. The stator, however, has no taper in the internal diameter, which is disposed in the region of the knurled feature.

[0004] From the book entitled “Feinmechanische Bauelemente” [“Precision-Mechanical Components”] by Prof. Dr.-Ing. S. Hildebrandt, Carl Hanser Verlag, Munich, page 221, it is known to use a shaft with a knurled feature; the knurled feature has an external diameter larger than an internal diameter of a component that is slipped onto the shaft in the region of the knurled feature and secured there. The component is mechanically softer than the shaft and presses into the knurled feature of the shaft, resulting in a reinforcement by positive engagement. Outside the knurled feature, the external diameter of the shaft is smaller than the internal diameter of the component.

[0005] U.S. Pat. No. 4,339,873 shows a rotor shaft that has an indentation in which a knurled feature is disposed. The component that is slipped onto the rotor shaft is disposed with its taper in the region of the knurled feature, in the installed state. The taper, however, is created by plastic deformation of the component, after the component has been slipped onto the shaft.

ADVANTAGES OF THE INVENTION

[0006] The armature of the invention as defined by the definitive characteristics of claim 1 has the advantage over the prior art that in a simple way, a component can be secured on a shaft and securely held. Also, because of the taper in the internal diameter of the component, the material of the component deforms plastically in the region of the taper and flows into the knurled feature and thus develops a positive engagement.

[0007] For the component, a plastic injection-molded magnet can advantageously be used, since this magnet is mechanically softer than the shaft.

[0008] It is also advantageous that the taper is disposed centrally in the component, because as a result the stresses can decrease uniformly all the way around the knurled feature.

DRAWING

[0009] One exemplary embodiment of the invention is shown in simplified form in the drawing and described in further detail below.

[0010] Shown are

[0011]FIG. 1, a component that is used for an armature of the invention;

[0012]FIGS. 2a, b and c, a shaft of the kind used for the armature of the invention, showing how it is produced;

[0013]FIG. 3, an armature of the invention in the assembled state.

DESCRIPTION OF THE EXEMPLARY EMBODIMENT

[0014]FIG. 1 shows a component 1, which by way of example is a mechanical ball bearing or a plastic injection-molded magnet and which is of a relatively softer material than the shaft 10 (FIG. 2).

[0015] The component 1 has a center axis 3, which by way of example can also be the axis of symmetry, and a recess 4, which extends axially in the interior of the component 1. A taper 7 is disposed in the axial direction, for instance centrally, in the recess 4 of the component 1; that is, in the outer region of the recess 4, the component 1 has an internal diameter Di, while in the region of the taper 7 it has a smaller internal diameter di.

[0016]FIG. 2c shows the shaft 10 of the armature of the invention, with an external diameter d′a.

[0017] The shaft 10 is produced for instance as follows. In the case of a shaft 10 with an external diameter Da, a plunge cut is made in the region 13 of a later knurled feature 11, and this plunge cut then has a smaller external diameter da (FIG. 2). The knurled feature 11 is made in this region, as shown in FIG. 2b. The knurled feature 11 has an outer external diameter d′a. The type of knurled feature is arbitrary. It can comprise longitudinal grooves, transverse grooves, or cross-hatched grooves.

[0018] The external diameter Da on the shaft 10 outside the knurled feature 11 is ground down or ground off on a lathe, as needed, such that it is equivalent to the external diameter of the knurled feature 11; that is, the shaft 10 has a constant external diameter d′a. Optionally, a knurled feature 11 that has an external diameter larger than Da is reduced to Da.

[0019] The shaft 10 can also be hardened intermittently.

[0020]FIG. 3 shows how the component 1 is secured to the shaft 10. The component 1 has an axial length that is longer than the knurled feature 11.

[0021] The internal diameter Di of the component 1 is for instance approximately equivalent to the external diameter d′a of the shaft 10 in FIG. 2c; that is, when the component 1 is initially slipped onto the shaft 10, the component 1 is guided by the shaft 10. There can also be a slight press fit. When the component 1 is slipped farther onto the shaft 10, a stress occurs, or is increased, in the component 1, since the taper 7 is slipped onto the shaft 10 outside the knurled feature 11. When the component 1 is displaced farther onto the shaft 10, until the taper 7 is disposed in the region of the knurled feature 11, the component 1 is deformed as a result of the press fit in the region of the taper 7, since the material comprising the component 1 penetrates the indentations in the knurled feature 11.

[0022] When the component 1 is guided by the shaft 10 in the region around the knurled feature 11, no notch stresses occur at the edges of the knurled feature 11; instead, the course of stress is as shown in FIG. 3, with a uniform drop in the stresses in the component 1 in both axial directions around the knurled feature 11. Over the course of time, a stressless state can even occur in the region of the former taper 7, and by then the component 1 is secured to the shaft 10 only by positive engagement.

[0023] Such an armature 15 can be used for an electric motor or an electric generator and, in a manner not shown, it has a carrier body for at least one coil or permanent magnets and for instance a commutator. 

1. An armature for an electrical machine, comprising a shaft, which at least in part has at least one knurled feature and at least in part, in the non-knurled places, has the same external diameter as the knurled feature; and at least one component, which is secured to the shaft by the knurled feature by means of a press fit, characterized in that the component (1) has a center axis (3); the component (1), in the interior, has an axially extending recess (4); and the component (1) at least in part has a taper (7) with an internal diameter (di), and the taper (7) is disposed in the region of the knurled feature (11).
 2. The armature of claim 1, characterized in that the component (1) is a plastic injection-molded magnet.
 3. The armature of claim 1, characterized in that the component (1) is a bearing.
 4. The armature of claim 1, characterized in that the taper (7) is disposed axially centrally in the component (1).
 5. The armature of claim 1, characterized in that the electrical machine is an electric motor.
 6. The armature of claim 1, characterized in that the electrical machine is an electric generator. 